Up to now, the liquid permeable surface layer of such articles has generally been composed of a fiber fabric web. Preferably, a web of this type should have no liquid absorbency but should only be capable of permitting the flow of fluid into the absorbent core accommodated inside it. Furthermore, the liquid permeable surface layer constituting the web facing the wearer's skin during use of the article should preferably be made soft, smooth and airy although with a sufficient degree of tensile strength.
The important demand on such a body-contacting diaper surface layer to be soft, airy and non-irritating to the wearer's skin has been recognized since long, for example through the European patent application No. 0 059 498 teaching an absorbent article with a liquid permeable surface layer consisting of a laminate composed of two different webs of which one is made from unbonded thermoplastic fibers and the other from a fiber fabric or net for example, constituting a web serving to support the first-mentioned layer. The thermoplastic fibers in the first-mentioned layer are melt bonded to the other layer or supporting web, preferably in a bonding pattern formed of crossing lines creating a diamond pattern. The purpose of such a laminate is to accomplish a soft body contacting surface layer without skin irritating effects, promoting simultaneously a rapid through-flow of body fluids into the absorbent core of the article.
The tensile strength of an unbonded fibrous layer is however known to be extremely poor even when bonded to a supporting web as is the case with the aforementioned prior art laminate. The risk of tearing or shedding fibers associated with this type of material is obvious unless, as a precaution, the bonding pattern for the supporting web is given a sufficiently close structure. The closer the bonding pattern, the stiffer, more awkward and less liquid impermeable the laminated surface layer thereby making it unsuitable for its purpose.
The handling and transport problems associated with unbonded fiber web are additional disadvantages in the manufacture of absorbent articles such as diapers.
The most common absorbent material used for absorbent products of the diaper type is so-called cellulose fluff pulp consisting of numerous short fibers which for obvious reasons are difficult to keep together into a coherent absorbent core. This factor is most crucial during mechanical treatment of the fibers. When using a disposable diaper with an absorbent core made of cellulose fluff pulp, the absorbent core is for example liable to burst causing the fibers included therein to lump and leaving in this manner large portions of the diaper completely void of absorbent material. This unfortunate effect of the low cohesiveness in cellulose fluff pulp fibers is generally most noticeable in the diaper crotch portion, that is the region of the diaper intended during use to be applied between the wearer's legs, which is the area exposed to maximum mechanical stress occurring in response to the movements of the wearer. This is also the area receiving the major part of urine discharged during use of the diaper. The fact that the absorbent material tends to burst most often in this specific area thus constitutes a serious drawback.
In order to stabilize and strengthen such absorbent cores for increasing their cohesivity during use there is previously known the technique of gluing the two surface layers encasing the absorbent core directly onto the absorbent material. Gluing in this manner can be performed for example by spraying or extruding a thin latticed layer of hot melt adhesive over the absorbent core or the surface layers prior to uniting them.
By gluing the liquid permeable surface layer to the absorbent core there is further provided a close contact between the surface layer and the absorbent core increasing in this manner the speed at which the body fluid enters the absorbent core since the body fluid is then immediately sucked up by the absorbent material substantially unimpeded by the surface layer.
However, as a result of the close relationship between the liquid permeable surface layer and the absorbent core, the body fluid contained in the absorbent core will come in direct contact, via the surface layer, with the diaper surface facing the wearer's body, which is a most significant drawback. As a consequence, the diaper surface layer will feel wet to the wearer when the absorbent core is soaked. In addition, the more or less intimate contact between the wet surface layer and the wearer's skin will prevent this area from being sufficiently ventilated. The tight fit of the absorbent core to the wearer's skin and the poor ventilation possibilities are factors which will finally increase the risk of chafing and skin irritation. Because of the humidity prevailing underneath the diaper due to discharge of urine and transpiration, the skin will moisten making it extremely sensitive to redness and irritation when exposed to mechanical forces. Skin irritation easily occurs especially as a result of chafing and poor ventilation in diapers provided with elastic members sealing tightly around the wearer's thighs. The elastic members of such diapers are generally applied to either side of the absorbent core and are fixed by gluing between the diaper surface layers which are joined together beyond the longitudinal edges of the absorbent core. In order to prevent the absorbent material from forcing its way out between the two surface layers, these layers must be fully glued together by means of hot melt adhesive for example, as hereinbefore described. However, such gluing will make the diaper edges rather stiff thereby creating sharp and chafing pleats at the location of the elastic members.
Accordingly, it has been found difficult so far to achieve a liquid permeable surface layer for absorbent articles with a satisfactory function in all respects. The more or less contradictory demands placed on such a layer with regard to softness, smoothness, surface dryness, airiness and strength are difficult to fulfill with the use of one and the same material, as appears from the foregoing. In case the liquid permeable surface layer also has to be secured to the absorbent core for the reinforcement thereof, and in order to provide for satisfactory liquid transport into it, the demands on user's comfort have not been possible to meet until now.